In this type of scenario it is usually necessary to take into consideration the power supply wattage and the consumption after the latest changes made to your system. The specifications of the graphics card suggest a minimum of 400 W from the power supply but this depends on the total amount of devices connected to your system.
I would suggest removing one of the components at a time (graphics or RAM) and test for results. You could also test the components in a different system or upgrade your power supply unit if needed.
There is also the chance of a compatibility issue since you are installing a new graphics adapter in an older system; updating the motherboard BIOS may help.